Over 70 million Africans and an even greater number of farmers in the Indian sub-continent will suffer catastrophic floods, disease and famine if the rich countries of the world fail to change their habits and radically cut their carbon emissions.

The stark warning, contained in a private Government document commissioned by Gordon Brown, comes days ahead of an announcement that will show Tony Blair backing away from his promise to "lead internationally" on climate change. The Government has decided to delay setting targets for industry to cut carbon emissions until other EU governments set theirs. Previously, Mr Blair has made a virtue out of leading the way in Europe.

The bleak facts on how climate change threatens the third world were laid out in a briefing paper drawn up this month by the Department for International Development. It pointed out that a quarter of Africa's population lives within 100km of the sea coast. As sea levels rises, when global warming melts the ice pack, the number of Africans at risk from coastal flooding will increase from one million in 1990 to 70 million in 2080.

In India, rising temperatures could drive down farm incomes by as much as a quarter, while the cost to Bangladesh of changes in the climate could be more than half the £58bn that country has received in foreign aid.

"It's the poorest people in the world who suffer from climate change, but they are the least responsible for it." John Magragh, of Oxfam, said yesterday.

The report emphasises that - despite the recent focus on New Orleans after Hurricane Katrina - 94 per cent of all natural disasters, and 97 per cent of deaths from natural disasters, occur in the developing countries.

All the work that aid agencies do to end hunger, improve education, combat disease, and close the gender gap will be jeopardised, the report warned. In Bihar, India, for example, flooding can shut schools across the state for three months of the year. Flooding caused by Hurricane Mitch brought a sixfold increase in cholera in Nicaragua. Mozambique's annual economic growth dropped from 8 per cent to 2 per cent in a year after a cyclone.

The briefing paper was drawn up for a review ordered by Gordon Brown into the economic impact of climate change. It was made public after a request by the BBC made under the Freedom of Information Act. The review team, headed by Sir Nicholas Stern, will report in the autumn. Sir Nicholas has already warned that climate change could push millions back into poverty, or force them to migrate.

Meanwhile, environmental agencies will focus their attention on next Tuesday's publication of the Government's climate change programme. A spokesman for the Environment department, Defra, said that the programme will contain "measures that will affect every sector of the economy" and said that the UK already has "one of the best records in the world" for combating climate change.

But the announcement could run into criticism from environmentalists for failing to specify targets on business to cut carbon emissions. This is the outcome of a battle between the Environment Secretary, Margaret Beckett, who wanted strict targets, and the Trade secretary Alan Johnson, who warned about the consequences for the competitiveness of British firms. The outcome is there will be no targets in next week's announcement.

The decision has angered the former environment minister, Michael Meacher. "Britain once led the EU and the world in our targets and our radical policies to tackle climate change. It's very disappointing that we seem to be holding back now to see what the rest of Europe is doing before we make up our minds."

Labour's general election manifesto last year singled out climate change as "one of the most pressing challenges that the world faces" and promised: "We will continue to lead internationally on climate change."

But the UK's carbon emissions, which had been falling since 1990, are now three per cent higher than when Labour came to power in 1997. This week, Gordon Brown announced that he is going to increase the climate change levy, which penalises businesses that produce high levels of carbon emissions, but it is thought unlikely that next week's programme will include any other increases in 'green' taxes.

Heating up

* By 2025, China will overtake the US as the leading emitter of greenhouse gases. It is already the world's biggest driver of deforestation.

* Current levels of carbon dioxide are higher than at any time in the past 650,000 years.

* Last year, the thermometer reached 50C (122F) in India, Pakistan, Bangladesh and Algeria.The northern hemisphere is warmer than it has been for 1,200 years. Temperatures are expected to rise by 6C in some places by 2100.

* The UK will fail to hit its 2010 target of reducing carbon emissions by 20 per cent on 1990 levels. The Government predicts a cut of 10.6 per cent.

* 2005 was a record year in the intensity and frequency of tropical storms: 26, compared with 21 in 1933. Fourteen were hurricanes. Hurricane Wilma was the strongest on record.